There was "nothing abnormal" in the final communication between the pilots of crashed Malaysian jet and air traffic control, authorities said today as Australia warned the search for wreckage of the ill-fated plane could be long and frustrating.

The full transcript of Flight MH370 released by Malaysian authorities confirmed that the final sign off was "Good Night Malaysian Three Seven Zero" not the casual "All Right, Good Night" as earlier reported.

"Today we are releasing the full transcript of communications between flight MH370 and Air Traffic Control Kuala Lumpur," Acting Transport Minister Hishammuddin Hussein said in a press statement.

"There is no indication of anything abnormal in the transcript," the statement said.

The transcript was initially held as part of the police investigation after the Beijing-bound Malaysia Airlines plane went mysteriously missing on March 8 after its take-off from Kuala Lumpur, with 239 people on board.

While there is nothing unusual about the new version of the final communication, the sudden change gives loved ones of the people aboard new suspicions that Malaysian officials are not giving them full and accurate information.

Previously, Malaysia Airlines had stated initial investigations indicated that the voice which signed off was that of the co-pilot Fariq Abdul Hamid and not the pilot Captain Zahari Ahmad Shah.

The police are working to confirm this belief, and forensic examination of the actual recording is ongoing, the statement said.

The international investigations team and the Malaysian authorities remain of the opinion that, up until the point at which it left military primary radar coverage, the Boeing 777-200's movements were consistent with deliberate action by someone on the plane, it said.

Meanwhile, multinational search teams were racing against time to locate the black box of the crashed airliner in southern Indian Ocean, with the frustrating search for the missing jet entering its 24th day today.

The clock was running out on plane's black box pingers as the batteries of the flight recorders - that have a life of about 30 days - will shut down in about eight days.

Retired Australian Air Chief Marshal Angus Houston, who is heading a new Joint Agency Co-ordination Centre (JACC) in Perth managing the search, said it was the most challenging search and rescue operation he had ever seen and warned efforts to trace the wreckage could take time.

He said task was "very complex", "very demanding" because the teams had no hard information to work from.

"It's not something that will necessarily be resolved in the next two weeks, for example," Houston said.